1. Technical Field
The present invention relates to a technique of detecting a change image, which has changed when compared with a temporally previous image, among a plurality of images arranged in time series.
2. Related Art
A moving image display system of performing projection display of a moving image by transmitting moving image data from a computer to a projector through a wireless LAN or the like is known. As such a moving image display system, a system of transmitting only a part of moving image data in order to reduce the amount of data transmitted from a computer to a projector has been proposed (refer to JP-A-2005-33763).
In the system disclosed in JP-A-2005-33763, each frame image, which forms a moving image, is compared with an immediately preceding frame image and then it is determined whether or not there is a change (difference). Then, if it is determined that there is a change, image data of a rectangular area including the entire difference region is transmitted from a computer to a projector. In the system having such a configuration, the amount of transmitted data may be reduced. However, since each frame image is compared with a previous frame image, it takes a very long time until detection of a change and transmission of image data are completed. Particularly in the case of capturing a moving image displayed on a display for a computer and transmitting the captured moving image to a projector, frame images to be compared are captured from a VRAM (video RAM), which is used for display on a display, sequentially to a general-purpose memory and are then compared with each other. In this case, since a VRAM that operates relatively slowly serves as a bottleneck, it takes a relatively long time to capture and compare frame images. As a result, it takes a very long time until transmission of image data of a change portion is completed.
In addition, the above-mentioned problem may occur in a case of performing data transmission of an image (hereinafter, referred to as a ‘change image’), which has changed when compared with a temporally previous frame image, to an arbitrary image display device without being limited to a projector. Furthermore, the above-mentioned problem may occur in a case of transmitting a plurality of arbitrary images arranged in time series, such as images that can be obtained by continuous shooting of a digital still camera, without being limited to the moving image. Furthermore, even in a system of performing only detection of a change image without performing data transmission of the change image, the problem that a long time is required until detection of the change image is completed may occur.